A circulator is often used with other optical devices to achieve certain optical functions. For example, a circulator can be used with a Brag Grating to extract an optical signal with a particular wavelength from a WMD optical signal. When an optical device such as a Brag Grating is manufactured using Planar Lightwave Circuit (“PLC”) or optical waveguide technologies, the optical device can become polarization sensitive. One method of using a PLC as a polarization insensitive device is to combine the PLC with a Polarization Maintenance (“PM”) circulator. FIGS. 1a and 1b illustrate a four-port PM circulator 50 coupled to a PLC 60 through two PM fibers 82 and 84.
As shown in FIG. 1a, a randomly polarized signal S1 received at port 1 of PM circulator 50 is separated into light beam 13 with the x-polarization and light beam 14 with the y-polarization. Light beam 13 exits from port 3 of PM circulator 50 and becomes signal S3 with the y-polarization. Light beam 14 exits from port 4 of PM circulator 50 and becomes signal S4 with the x-polarization. Signal S3 is transmitted into PLC 60 through PM fiber 82. Signal S4 is transmitted into PLC 60 through PM fiber 84.
As shown in FIG. 1b, optical signal S3′ with the y-polarization, received from PLC 60 through PM fiber 82, enters port 3 of PM circulator 50 as light beam 32. Optical signal S4′ with the x-polarization, received from PLC 60 through PM fiber 84, enters port 4 of PM circulator 50 as light beam 42. Light beam 32 exits from port 2 of PM circulator 50 as a first component of signal S2 with the x-polarization. Light beam 42 exits from port 2 of PM circulator 50 as a second component of signal S2 with the y-polarization.